The present invention relates generally to a biocidal composition that releases chlorine dioxide. The invention particularly relates to a composite for reducing bacterial, fungal, and viral contamination and for killing mold spores.
Chlorine dioxide (ClO.sub.2) is a superior oxidizing agent widely used as a bleach, disinfectant, fumigant or deodorizer. It can penetrate the cell wall or membrane and cytoplasm of mold spores, bacteria and other microbiological contaminants at concentrations below one part per million and destroy them.
The incorporation of chlorine dioxide or sodium chlorite in food packaging has prompted studies to determine whether residual levels of such preservatives result in a significant genetic or carcinogenic hazard to humans. Meier et al. studied the effect of subchronic and acute oral administration of chlorine, chlorine dioxide, sodium chlorite and sodium chlorate on the induction of chromosomal aberrations and spermhead abnormalities in mice [Environ. Mutagenesis, 7, 201 (1985)]. Only the highly reactive hypochlorite resulted in a weak positive effect for mutagenic potential. The other compounds, including chlorine dioxide and sodium chlorite, failed to induce any chromosomal aberrations or increased numbers of micronuclei in the bone marrow of mice. Vilagines et al. attribute the relatively innocuous effect of chlorine dioxide to its inability to produce halomethanes, unlike hypochlorite and chlorine [Proc. AWWA Disinfect. Semin., 24 pp. (1977); Chem. Abs. 93, 173513f]. Recently, Richardson et al. reported that an extensive study of the reaction of chlorine dioxide with water borne organics by the Environmental Protection Agency confirmed this observation [Environ. Sci. Technol., 28, 592 (1994)].
Japanese Kokai Nos. 63/296,758, 63/274,434, and 57/168,977 describe deodorants containing chlorine dioxide incorporated in a polymer, ceramic beads, or calcium silicate wrapped in nonwoven cloth, respectively. Gels that generate chlorine dioxide for use as topical applications for disinfection are disclosed by Kenyon et al., Am. J. Vet. Res., 45(5), 1101 (1986). Chlorine dioxide generating gels are generally formed by mixing a gel containing suspended sodium chlorite with a gel containing lactic acid immediately prior to use to avoid premature chlorine dioxide release. Chlorine dioxide releasing gels have also been used in food preservation.
Encapsulation processes have also been used in preparing sources of chlorine dioxide. Canadian Patent No. 959,238 describes generation of chlorine dioxide by separately encapsulating sodium chlorite and lactic acid in polyvinyl alcohol and mixing the capsules with water to produce chlorine dioxide.
Tice et al., U.S. Pat. No. 4,585,482 describe gradual hydrolysis of alternating poly(vinyl methyl ether-maleic anhydride) or poly(lactic-glycolic acid) to generate acid which can release chlorine dioxide from sodium chlorite. A polyalcohol humectant and water are encapsulated with the polyanhydride or polyacid in a nylon coating. After sodium chlorite is diffused into the capsule through the nylon wall, an impermeable polystyrene layer is coacervated around the nylon capsule. Solvents are required for reaction and application of the capsules. The capsules can be coated onto surfaces to release chlorine dioxide. Although the capsules are said to provide biocidal action for several days to months, chlorine dioxide release begins immediately after the capsules are prepared. The batchwise process used to prepare the capsules also involves numerous chemical reactions and physical processes, some of which involve environmental disposal problems.
There is a need for an inert composition that can be easily activated to initiate chlorine dioxide release in use. A composition that is composed of and generates only FDA approved substances, or those generally recognized as safe, is particularly needed for food packaging and other applications where the substances can be ingested by or in contact with humans.